A Novel Marker for Predicting Fulminant Myocarditis: Systemic Immune–Inflammation Index

In myocarditis, the search for effective and appropriate prognostic biomarkers can help clinicians identify high-risk patients in a timely manner and make better medical decisions in clinical practice. The prognostic value of systemic immune–inflammatory index (SII), an innovate biomarker of inflammation, in fulminant myocarditis in children has not been assessed. This study aims to (1) determine the effect of SII and other inflammatory markers on the prognosis of patients with myocarditis, and (2) characterize other factors affecting adverse outcomes in myocarditis. All patients aged between 1 months and 18 years who admitted to Pediatric Emergency Department between January 1, 2015 and October 1, 2021 and were diagnosed with myocarditis were retrospectively analyzed. 106 Eligible subjects were enrolled (67% male, 12.5 years (IQR 6–16). Fulminant myocarditis developed in 16 (15%) of the patients. The median SII was 1927 (1147.75–3610.25) in the fulminant myocarditis group and 351 (251.75–531.25) in the non-fulminant group (p < 0.001). In estimation of fulminant myocarditis, AUC was 0.87 for WBC [95% confidence interval (CI) 0.72–1.00, p = 0.002], 0.94 for ANC (95% CI 0.85–1.00), p = 0.000), 0.92 for SII (95% CI 0.82–1.00, p = 0.000). Spearman’s correlation analysis showed a significant negative correlation between SII and LVEF (r = 0.576, p < 0.001). The highest AUC values were associated with ANC, SII, and WBC levels to predict fulminant myocarditis. SII, a readily available biomarker from routine blood parameters, allows early recognition of negative outcomes and can independently predict the prognosis of myocarditis in children.